The pouring of a molten material, such as metal, for example, into a casting mold is a significant process variable that influences the internal soundness, surface conditions, and mechanical properties, such as tensile strength, porosity, percent elongation and hardness, of a cast object. Many different designs for dipping/pouring ladles exist and are used in the foundry industry. The designs are normally chosen based upon the type of molten material and casting mold used. Commonly used ladles make use of a slot, a lip and a baffle, or a dam at the top of the ladle to reduce inclusion of furnace metal oxides during metal filling, or the ladle may incorporate a stopper rod to control the flow of metal into and out of the ladle.
Molten metals, such as aluminum, for example, react with the air and create oxides, commonly known as dross, which upon mixing with the rest of the molten metal creates inclusions and highly porous regions in the cast object during solidification of the metal. While many factors influence and account for undesirable properties in the cast object, two common sources of inclusions include formation of a dross layer on top of the molten metal, and the folding action of the molten metal caused by turbulent flow of the molten metal during pouring. Turbulent metal flow exposes the molten metal surface area to the air which creates the dross layer. Depending on the velocity of the molten metal, dictated by the pouring ladle and basin design and use, the molten metal may fold-over itself many times, thereby trapping oxygen and metal oxide layers therein and exposing additional surface area of the metal to the air.
Typical foundry ladles are referred to as teapot-type ladles. These ladles are substantially cylindrical in shape with an external spout extending outwardly from the top thereof. Certain teapot ladles have incorporated a wall or a baffle to separate the bowl or cavity area of the ladle from the spout. The wall or baffle may extend to the bottom of the ladle. When the molten metal is poured, the baffle restricts the flow of molten metal from the top of the ladle to facilitate the pouring of the metal that is near the bottom of the ladle. The metal at the bottom of the ladle is substantially free from dross and other foreign material that may be present, such as eroded refractory lining and ash created during a melting process of the metal. Although the baffle serves to minimize dross inclusion, the external spout design still increases the velocity of the material upon pouring, and may create turbulent flow. Next, the molten metal is typically transferred from the ladle to a casting mold through a pour basin. In traditional pour basin designs, molten material flows down the basin to a mold sprue. The flow of the molten metal through the sprue may also cause turbulence therein, thereby creating additional dross.
Low pressure, bottom pour furnaces have been known to produce castings with minimized dross, but the equipment is expensive, complex, and subject to high maintenance requirements. In addition, the bottom pour furnaces increase capital costs. Hot Isostatic Pressing (HIPping) of castings may also reduce porosity in aluminum castings, however HIPping is expensive and may cause dimensional changes to the casting that may not be uniform or replicable.
Thus, there remains a need for an economical method and apparatus that would prevent or minimize the inclusion of dross and contaminants leading to high porosity and/or low mechanical properties of cast materials.
It would be desirable to provide an apparatus and method for the quiescent-fill of a ladle and the transfer of a molten material from the ladle to a casting mold to minimize turbulence in the molten material to minimize defects in the desired cast object formed by a tilt pour molding process.